Our long-term goal is to study the role of mitochondria in aging. The overall goal of this grant application is to test the mitochondria! theror/ of aging and, in particular, to investigate the role of mitochondrial DNA(mtDNA) mutations in mouse brain during aging. As one of the most favored hypotheses, the mitochondrial theory of aging, predicts that somatic mitochondria DNA (mtDNA) mutations accumulate with time, and the compromised mitochondrial function resulting from these mutations is then responsible for various aging phenotypes. However, there has been no comprehensive study of the overall accumulation of mtDNA mutations during aging, and the physiological consequences of aging-related mtDNA mutations are largely unclear. We recently established a method to transfer mtDNA from mouse nerve endings, i.e., synaptosomes to a cell system, and we have improved methods to isolate and characterize mtDNA mutations. Combined with established mitochondrial molecular genetic and biochemical technologies, we can, for the first time, investigate the accumulation of mtDNA mutations in neuronal cells during aging by evaluating individual mtDNA from the synaptosomes.The particular hypothesis to be tested in this proposal is that mutations in the mitochondrial genome accumulate during aging in mouse neuronal cells;these mtDNA mutations in turn compromise mitochondrial function and may result in oxidative damage to various cellular components including mtDNA in neuronal cells. We will perform genetic and functional analyses of aging-related mtDNA mutations by transferring synaptosomal mtDNA to a cell line system. This will reveal low frequncy mtDNA mutations that could not be identified by other methods. By generating neuronal cell models that carry aging-related mtDNA mutations, we will also charaterize the physiological consequences of the mutations, in particular those related to oxidative damage. The successful completion of this project will not only help to test the mitochondrial theory of aging, but could also provide insights into the underlying mechanisms of the aging process.